1. Field of the Invention
The present invention relates generally to digital-to-analog converters (DACs), and more specifically, to noise reduction in a DAC having a chopper amplifier output stage.
2. Background of the Invention
Chopper amplifier output stages are frequently used to provide an analog output from digitally-switched circuits. The use of a chopper reduces or eliminates the effect of offset voltages and flicker noise at the chopper amplifier by effectively modulating the lower frequency range, including DC, to a frequency range that is easily removed by an analog filtering stage. The filtering stage either forms part of the response of the chopper amplifier or is provided in a successive analog filter stage. The chopping frequency effectively modulates the DC offset to multiples of the chopping frequency.
However, broadband noise or other noise sources that have a component near a multiple of the chopping frequency will similarly be aliased to an in-band frequency that increases the noise level of the DAC.
Therefore, it would be desirable to provide an improved DAC having a chopper amplifier output stage with reduced noise. It would be further desirable to provide such an improved DAC at low incremental cost.